[Neuromuscular recovery following mivacurium is predictable in patients with severe systemic disease prognoses]

Fast recovery from mivacurium-induced neuromuscular blockade is impaired in patients with decreased plasma cholinesterase activity which is often associated with dysfunction of different organs. Nevertheless, predictability of neuromuscular recovery may be given. Thus, this study evaluates parameters to predict individual neuromuscular recovery in patients with uncommon diseases.

84 male or female patients (18-70 years of age) were allocated to one of two groups according to their ASA risk profile (without severe systemic diseases: ASA 1 and 2; with severe systemic diseases: ASA 3 and 4). Plasma cholinesterase activity (PChE) had been determined preoperatively. Anaesthesia was performed with propofol and fentanyl. Neuromuscular transmission was monitored by electromyography. The ulnar nerve was stimulated by train-of four stimuli and neuromuscular transmission was measured at the hypothenar. After mivacurium 0.1 mu mg/kg, an infusion of mivacurium was adjusted to maintain T1/T0 at approximately 5% for at least 60 min. Duration from application of the initial bolus until recovery to T1/T0 = 5% (dur 5), the mean mivacurium infusion rate (IR), infusion time, the early recovery time from cessation of infusion to T1/T0 = 25% (rec 25) and the final recovery time from T1/T0 = 25% to T4/T1 = 75% (final rec) was measured. Statistical analysis of data was performed using t-tests. (alpha = 0.05). Predictability of the recovery times (rec 25 and final rec) was tested by multiple linear least-squares regressions. Dependent variables were PChE, dur 5, IR, infusion time, and rec 25, respectively. To test for predictability of neuromuscular blockade by mivacurium with respect to severe systemic diseases, the ASA risk score was defined to be the second independent variable at each regression, the respective interaction was defined to be the third independent variable (variable 1 x group). Variables entered multiple regression analysis in a forward stepwise manner (F > 4.0).

PChE was significantly lower in patients with severe systemic diseases (3.7 +/- 1.2 kU/l vs. 4.5 +/- 0.9 kU/l), dur 5 significantly prolonged (17.3 +/- 7.3 min vs. 11.0 +/- 3.0 min), IR significantly lower (4.6 +/- 2.6 micrograms/kg/min vs. 6.5 +/- 2.8 micrograms/kg/min), and rec 25 (8.7 +/- 4.0 min vs. 6.0 +/- 1.7 min) as well as final rec (23.0 +/- 16.3 min vs. 13.0 +/- 3.7 min) significantly prolonged compared to patients without severe systemic diseases. Both recovery intervals correlated significantly with PChE, dur 5, or IR, but not with the ASA risk score. Multiple regression analysis revealed a close correlation between rec 25 and final rec very closely (R2 = 0.875). Prolonged mivacurium infusion time and additionally high ASA risk score were correlated with a prolonged neuromuscular recovery (R2 = 0.130).

Prolonged neuromuscular recovery could be predicted from a reduced PChE, a prolonged duration of action of the initial mivacurium bolus and a decreased mivacurium-infusion rate required to maintain a 95% neuromuscular blockade. Measurement of plasma cholinesterase and monitoring of mivacurium induced neuromuscular blockade can avoid resting neuromuscular blockade postoperatively despite of prolonged neuromuscular recovery.